Race For Water Odyssey: Quantitative and Qualitative Assessment of Marine Plastic Debris Collected on Shorelines

With the help of the local people we met during the course of the 2015 Odyssey, the main objective, obtaining a collection of comparable data about marine plastic pollution using the NOAA internationally recognized protocol, has been achieved. It cannot be sufficiently stressed that not one of the 30 sampled shorelines during this worldwide journey was free from marine plastic debris. As for the recent identification of plastic debris in the Arctic and Antarctic areas, this observation confirms that plastic contamination in the oceans is ubiquitous. Whether in terms of macrodebris (>2.5 cm) or microplastics (< 5 mm) concentrations, Hawaii constitutes by far the 2015 Odyssey’s most notable hotspot. The highest macrodebris concentration registered at Kamilo Point in Hawaii (more than 3,500 macrodebris per 100 m2) was almost ten times greater than the second hotspot of the 2015 Odyssey, Pago Bay (372) on Guam Island in the Mariana Archipelago. Hawaii also constitutes the highest microplastics concentration hotspot with more than 94,000 particles per m2 collected once again at Kamilo Point again. For comparison, the second highest concentration, Ovahe beach on Easter Island, revealed more than 24,000 microparticles per m2. Unfortunately, based on their locations, marine macrodebris concentrations can suffer bias due to direct waste disposal (intentional or accidental) of tourists and/or local residents, and also because of the consecutive shoreline clean-up campaigns. Therefore, microplastic concentrations are a more reliable indicator to establish a comparison between study sites. On that basis, Northeast Pacific islands – especially the Hawaiian Archipelago – experience the most significant marine debris accumulation, followed by those of the South Pacific, Northeast Atlantic, Indian, Northwest Atlantic, Northeast Pacific and South Atlantic Oceans respectively. The macrodebris and microplastic average concentrations are summarized below in Figure 1. In qualitative terms, the hard plastic fragments category largely dominates the macroplastics content except for Palau and Chagos (BIOT). Other dominant categories are plastic foams, bottles and caps, and fishing lines and ropes. Foams were particularly predominant in Chagos, while bottles and caps constituted almost 70% of macrodebris in Palau. Besides, significantly higher bottle and cap concentrations were evidenced near the Asian continent. Fishing lines and ropes stood out particularly in Bermuda. Microplastic concentrations confirmed these trends with more than 80% of hard plastic fragments on every stopover, except Easter Island and Tristan da Cunha (around 60%). More specifically, Easter Island showed a significant concentration of pellets, while Bermuda confirmed a strong presence of fishing lines among the microparticles. Lastly, the polymer analysis of the hard plastic fragments ranging from 1 mm to 2.5 cm revealed the prevalence of polyethylene (PE) throughout all of the study sites, except for Tristan da Cunha where polypropylene (PP) dominated. Hawaii, Mariana, Palau and Mascarene also showed significant PP concentrations (between 31 to 47% of items). Other kinds of polymer such as EVA and PMP, have been evidenced especially on Tristan da Cunha, but also on the Azores and Mariana.